Solvent fractionation



Jan. 5, 1937. w. B. KAY

soLvENT FRACTIONATION 'Filed July 22, 1955 2 Sheets-Sheet 2 mm. wm.

@MM5 w05 mod WN NN J Y mK T. KR mw Lm V Q .Num A m E Y Patented Jan. 5, 1937 UNITED STATES SOLVENT FRACTIONATION Webster B. Kay, Chicago, Ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana 'Application July 22, 1935, Serial No. 32,506

This invention relates to the fractionation of lubricating oil stocks and particularly to the fractionation of lubricating oil stocks by the use of propane or other liquefied normally gaseous hydrocarbon, preferably in the presence of an organic selective solvent such as cresylic acid. It further relates to certain new and useful pressure effects relating to fractionation processes of the type mentioned.

It is an object of my invention to provide certain new and novel processes for the fractionation of lubricating oils by the use of mixtures of liquefied normally gaseous hydrocarbons and organic selective solvents operating in a newly discovered phase separation zone, operation in which permits the use of lower temperatures than have hitherto been possible for this type o f operation. Another object of my invention is to provide processes for the countercurrent fractionation of lubricating oils in the presence of a liqueed normally gaseous hydrocarbon and preferably also in the presence of an organic selective solvent using pressure eiects to accomplish the fractionation in the various stages of the countercurrent process thereby eliminating the necessity of accomplishing this fractionation by expensive temperature variations. Other and more detailed objects of my invention will become apparent as the description thereof proceeds.

My invention will be described with particular reference to the accompanying drawings which form a part of this specification and in which:

Figure l is a pressure-temperature phase diagram illustrating the scientific basis for my invention, .and

Figure 2 is a conventionalized flow diagram illustrating one specific embodiment of my process.

Referring now more particularly to Figure 1, it will be seen that this is a pressure-temperature phase diagram for a system consisting of one part by volume of a heavy lubricating oil` known as steam refined oil, one part by volume of cresylic acid 'and 3.7 parts by volume of propane. Under most conditions of temperature and pressure these constituents in the proportions mentioned are completely miscible in each other and form only 'one liquid phase. Thus in the region below the line I0, indicated as Zone A, a vapor phase will exist in equilibrium with a liquid which will be a single phase throughout the area of zone A except-:for small'areas below zones C and D. When the pressure 4is increased to a value represented by` any point above line I0, the .vapor phase ceases to exist.

exists. However, there are two areas in which two liquid phases exist in the absence of a vapor phase and in which fractionation of the lubricating oil is therefore possible. Y

One of these areas is in the vicinity of the critical conditions of the propane or other liqueed normally gaseous hydrocarbon used. This area is indicated as zone C and it exists whether or not an organic selective solvent is present in addition to the lubricating oil and liqueed normally gaseous hydrocarbon. It will be noted that this zone C is separated from zone B by a line il which slopes upward and to the right. This means that in passing from zone B to zoneC the pressure at which two liquid phases form from one liquid phase in the absence of vapor increases with increasing temperature of the system.

Line l2 which separates zone B from zone D, slopes in a direction opposite to that of line Il, or in other words in passing from zone B to zone D the pressure at which two liquid phases form fromone liquid phase in the absence of vapor, decreases with increasing temperature of the system.

When no organic selective solvent is used with the propane or other liqueed normally gaseous hydrocarbon, or when the organic selective solvent is used alone without the liqueed normally gaseous hydrocarbon, line I2 is substantially Vertical and it is,'therefore, impossible to pass from zone B to zone D or vice versa by means of pressure changes.- In other words, when a solution of lubricating oil in a liquefied normally gaseous hydrocarbon or in an organic selective solvent is cooled, the temperature at which a second liquid phase starts to form is independent of the pressure on the system, whereas when both are present, this temperature varies considerably with the pressure. The discovery of this hitherto unappreciated and unsuspected phenomenon forms one of the important groundworks for my invention since it is possible to pass from zone B'to zone D or vice versa by pressure changes alone rather than by temperature changes. Since .the systems involved are liquid phase systems and since no vapor is present, pressure changescanbe effected with very slight ,volume changes and,

therefore, with the expenditurevef very little energy. y y

One of the former methods of fractionating lubricating oils bythe use'llof solve nts,.ha.s-in-A volved heating the oil andmsolvent above their miscibility temperature and then cooling them to 'uous countercurrent process.

2 separate two liquid phases. According to my invention, this result is more economically and ex peditiously effected by dissolving the oil in the solvent, bringing the solution to a high pressure and then lowering the pressure to a point within zone D, thereby precipitating two liquid phases.

This is particularly advantageous in a contin- Processes of this type may consist of from as few astwo or three stages up to as many as 8 or 10 stages. Each stage consists essentially of a contacting step and a separating step. The separatedmaterials ow in opposite directions to the contacting steps of the adjacent stages. A process of this type which utilizes temperature changes to secure complete, or at least increased, miscibility in the various contacting steps and which obtains separation by cooling (or miscibility by cooling and separation by heating when operating in zones B and C) involves the addition and removal of heat in each of the various stages. In accordance with my process, temperature changes are replaced by pressure changes and since the volumegchanges are very small the amounts of equinmentjaridfenf ergy required to eect these changes ar'esniallas" compared with the prior art processes operating by means of temperature changes.

Figure 2 of the drawings is a flow diagram showing one countercurrent process operating in accordance with my invention. In the process illustrated, four stages are used, each stage consisting of a contacting step and a separating step. A larger number of stages will often be advantageous.

In the rst stage, propane enters the system through line 20 and valve 2| and is passed through pump 22 along with an extract phase consisting of o il and cresylic acid from thesecond stage. The two streams undergo mixing in mixer 23. The pressure created by pump 22 may, in one preferred form of my process, be suiicient to create'complete miscibility. In other words, the

temperature and pressure conditions may suitably fall within zone B of Figure 1.

The mixed stream may then pass through heater or cooler 24 but this heater or cooler along with heaters or coolers 40, 43, and 54 may often be omitted. These heaters or coolers and their use will be discussed hereinafter.

'Ihe pressure of the stream is reduced on passing through reducing valve 25, to a point which will cause two liquidphases to form, i.v 'e to a point within zone D of Figure 1.

The two liquid phases thus formed are separated in separator A.

The extract phase settles to the bottom of separator A, which is preferably tilted and provided with extensions as shown, is removed through line -26 and passes through valve 21 into hash drum 28. Propane is removed through valve 29 and is recompressed and returned to line 20 by conventional means not shown.

The bottoms from flash drum 23 pass through pump 33 into bubble tower 3l provided with heating coil 32 and dephlegmating coil 33. 'Cresylic acid vapors pass overheadthrough valve 34, are condensed (by means not shown) and reintroduced into the system through line 52 as will hereinafter be described.

i The lubricating oil extract is removed from the base of tower 3l through valve 3.5 for further treatment and/or use as desired.

Returning now to separator A, the ramnate phase is removedl through valve 36 and passes lng to` elements through pump 31 along with the lubricating oil stock, which enters the system at this point through valve 33, and the extract phase from the third stage. The combined stream passes through mixer 33 and here again the pressure and temperature conditions may suitably be represented by a point falling within zone B of Figure 1.

The pressure is again reduced in reducingvalve 4I until two liquid phases form in the desired proportions. The temperature and pressure within separator B are represented by a point within zone D ofFigure 1.

The extract phase from separator B flows back through line 42 and valve 43 to the first stage of the process, while the rainate phase flows out through valve 44 and enters the third stage along with the extract phase from the fourth stage.

The third and fourth stages operate similarly to th first and second stages heretofore dealraffinate'phase 'from the fourth stage ato'rD) flows out through line 56 and valve "`51"td"`aflvent recovery system which is similar to that previously-described for the final extract phase; elements 58 to 64, inclusive, correspond- 28 to 34, inclusive, respectively. The raflinate hydrocarbons are removed from the base of tower 6l through valve 65 for further treatment and/or use as desired.

Instead of having only one stage (corresponding to separator D) subsequent to the introduc-l tion of the cresylic acid or other selective solvent it is often desirable to provide a plurality of such stripping stag "i Mixers 23, 39, 46, and 53 may, in many cases, be dispensed with since adequate mixing will generally occur in pumps 22, 31, 45, and 5|. However, the mixers are useful in that they insure uniformity of solution and tend to smooth out pulsations which may exist in the streams passing through them.

As described, my process comprises raising the pressure in each stage to the point of complete i miscibility and then lowering it to separate two liquid phases. Complete miscibility, however. is not essential and it is only necessary to somel. what increase the miscibility in order to secure thorough contacting before separation.

Heaters or coolers 24, 40, 48 and 54 and/or heaters and coolers otherwise located may be used to compensate for thermal changes incident to pressure changes and thereby render the process more accurately isothermal.

It will be seen that for the system of Figure l a processcan be operated isothermally at F. In each stage the pressure can be raised to about 600 lbs.per sq. in. to insure complete miscibility, but the pressure need not be that great. A pressureof 450 lbs. per sq. in. will give thorough contact without complete miscibility. The

Aseparation pressure should be well within zone D, e. g. 350 lbs. per sq. in.

My process need not, however, be strictly isothermal. Temperature changes may be used to assist and supplement the pressure changes on which I prefer to depend for my major phase separation eiects.

One particularly advantageous process using temperature changes to assist pressure changes may be operated by progressively decreasing the pressure from stage to stage. Thus, presuming (as is only'roughly the case) that the composi- 4tion of the system in each stage corresponds to that of Figure 1, the contacting step of the rst stage can be operated at 700 lbs. per sq.-in. and F., under which conditions the system is completely miscible. The pressure can then be lowered isothermally to 600 lbs. per sq. in., at which pressure two liquid phases will be present and can be separated. The contacting step of the second stage can then be operated at this same pressure but at 98 F., under which conditions complete miscibility is again secured. By lowering the pressure to 450 lbs. per sq. in. separation again takes place in this second stage. The contacting step of the third stage can be operated by raising the temperature to 103 F. without change in the pressure. Separation in this third stage can again be secured by lowering the pressure isothermally, this time to about 350 lbs. per sq. in. Miscibility in the contacting step of the fourth stage can then be secured by increasing the temperature at this same pressure to 107 F. and separation can be obtained in this fourth Stage by lowering the pressure isothermally to about 275 lbs. per sq. in. The process thus involves a series of isothermal pressure changes and isobaric f temperature changes, the course of which is indicated on Figure 1 by dashed line I3.

Operating as described in the last paragraph. pumping costs and heating costs are reduced to a minimum since the pressure is reduced from stage to stage and the temperature is increased only slightly from stage to stage. It is, of course, necessary to boost the pressure on the extract phase which is recycled to the preceding stage.

A similar process can also be operated working between zone B and zone C and in this case beth the pressure and the temperature will be reduced progressively.

It will be understood that in operating a process between zone B and Zone C or entirely in zone C it is not necessary to have cresylic acid or other organic selective solvent present since these zones exist for systems composed of lubricating oil and a liquefied normally gaseous hydrocarbon, such as propane.

I can also operate a process in which some of the stages effect separation under conditions falling within zone C and other stages effect separation under conditions falling within zone D.

It is to be understood, however, that I prefer, for reasons previously outlined, to operate my process in zone D or preferably working between zone B and zone D.

In place of propane, other liquefied normally gaseous hydrocarbons can be used. In the case of the fractionation of very heavy lubricating oils the use of butane is advantageous, while with very light lubricating oils the use of ethane is advantageous. I prefer to use the normal saturated hydrocarbons mentioned but it is also possible to use isobutane. I may also use, but do not prefer to use, the oleflnic hydrocarbons of 2, 3 or 4 carbon atoms per molecule. Although I prefer to use a single liquefied normally gaseous hydrocarbon in relatively pure condition it is also possible to use mixtures of the various liquefied normally gaseous hydrocarbons.

In place of cresylic acid, I may use the ortho, meta or para cresols. I may also use phenol or other phenolic compounds. substituted phenolic compounds, such as the chlorphenols, can also be used. Although the aforementioned organic selective solvents are preferred in'my process I can also use other organic selective solvents which have a preferential solvent power for the relatively naphthenic constituents of lubricating oils.

'gaseous hydrocarbon and organic selective solvent chosen. The proportions, as Well as the operating conditions, can readily be determined b1 .experiment ln the light of the principles lai down in this specification.

I prefer, however, to use for each volume of lu bricating oil stock from 0.1 to 5 volumes and prefl erably from 0.5 to 2.5 volumes of organic selectivn solvent (preferably cresylic acid) and from 0.! to 10 and preferably from 1 to 6 volumes of liq` uefied normally gaseous hydrocarbon (preferabl: propane). I also prefer that at least two an( preferably at least three volumes of liquetlel normally gaseous hydrocarbon be present fo 'each volume of organic selective solvent.

l While I have described my invention in con nection with certain specific embodiments there of and in connection with certain theories tl account for its operation it is to be understoo that these are by way of illustration rather thai by way of limitation and that I do not mean t1 be bound thereby but-only to the broadest valie sccpe of the appended claims in which I will de v ne the novel features of my processes.

I claim:

1. In a process for the fractionation of a sys tem comprising lubricating oil, a liquefied nor mally gaseous hydrocarbon and an organic se lective solvent, said system being characterizel by a pressure-temperature phase diagram i1 which an area in which one liquid phase and nl vapor phase exists is separated from an area ix which two liquid phases and no vapor phas exist by a line which slopes from a point of higl temperature and low pressure to a point of loi temperature and high pressure, the steps whicl comprise bringing said system to a temperatur and pressure represented by a point in said rst mentioned area and then lowering the pressur on said system to bring said system to a temper ature and pressure represented by a point in sai second-mentioned area.

2. Steps according to claim 1 in which said or garlic selective solvent is a phenolic compound 3. Steps according to claim l in which said or ganic selective solvent is cresylic acid.

4. Steps according to claim 1 in which sai organic selective solvent is cresylic acid and sai| liqueed normally gaseous hydrocarbon is pro pane.

5. In a countercurrent process for the frac tionation of a system comprising lubricating oi a liquefied normally gaseous hydrocarbon an an organic selective solvent. said system bein characterized by a pressure-temperature phas diagram in which an area in which one liqui phase and no vapor phase exists is separate from an area in which two liquid phases and n vapor phase exist by a linewhich represents substantial range of pressures, by means of a plu rality of stages. each of said stages consisting o a contacting step and a separating step, the im provement which consists in operating said contacting steps at pressures higher than those of the corresponding separating steps.

6. In a countercurrent processfor the fractionation of a system comprising lubricating oil, a liquefied normally gaseous hydrocarbon and an organic selective solvent, said system being characterized by'a pressure-temperature phase diagram in which an area in which one liquid phase and no vapor Aphase exists is separated from an area in which two liquid phases and no vapor phase exist by a line which represents a substantial range of pressures, by means of a plurality of stages, each of said stages consisting of a contacting step and a separating step, the improvement which consists in operating each of said contacting steps at a temperature and pressure represented by a point within said firstmentioned area and each of said separating steps at a pressure lower than that of the corresponding contacting step, the temperature and pressure of each of said separating steps being represented by a point within said second-mentioned area.

'7. Steps according to claim 6 in which each of said contacting steps is operated at a pressure substantially lower than that of the preceding contacting step.

8. Steps according to claim 6 in which each separating step is operated at a pressure substantially lower than that ofthe preceding contacting step and at a pressure substantially equal to that of the succeeding contacting step.

9. In a countercurrent process for the fractionation of a system comprising lubricating oil, a liquefied normally gaseous hydrocarbon and an organic selective solvent, said system being characterized by a pressure-temperature phase diagram in which an area in which one liquid phase and no vapor phase exists is separated from an area in which two liquid phases'and no vapor phase exist by a line which represents a substantial range of pressures, by means of a plurality of stages, each of said stages consisting of a contacting step and a separating step, the improvement which consists in operating each of said contacting steps at a pressure higher than that of the corresponding separating step and at a temperature substantially equal to that of the corresponding separating step.

10. In a countercurrent process for the fractionation of a system comprising lubricating oil,

a. liqueed normally gaseous hydrocarbon and an organic selective solvent, said system being characterized by a pressure-temperature phase da` gram in which an area in which one liquid phase and no vapor phase exists is separated from an area in which two liquid phases and no vapor phase exist by a line which slopes from a point of high temperature and low pressure to a point of low temperature and high pressure, the steps which comprise bringing said system to a temperature and pressure represented by a point in said firstmentioned area and then lowering the pressure on said system to bring said system to a temperature and pressure represented by a point in said second-mentioned area, separating the two liquid I phases thus formed, passing one of said two liquid phases to a preceding contacting step and passing the other of said two liquid phases to a succeeding contacting stop.

11i In a process for the Afractionation of a system comprising lubricating oil, a liquefied normally gaseous hydrocarbon and an organic selective solvent, said system being characterized by a pressure-temperature phase diagram' ln which an area in which one liquid phase and no vapor phase exists is separated from -an area in which two liquid phases and no vapor phase exist by a line which slopes from a point of high temperature and low pressure to a point of low temperature and high pressure, the steps which comprise bringing said system to a-temperature and pressure represented by a rst point vin said secondmentioned area, said point being near said line, to promote miscibility of the two liquid phases, and then lowering the pressure on said'system to bring said system to a temperature and pressure represented by a second point in said secondmentioned arca to promote immiscibility of said two liquid phases, and separating said two liquid 'phases under the conditions represented by said second point.

12. Steps according to claim 1l in which said organic selective solvent is a phenolic compound.

13. Steps according to claim 11 in which said organic selective solvent is cresylic acid.

14. Steps according to claim 11 in which said organic selective solvent is cresylic acid and said liquefied normally gaseous hydrocarbon is propane.

WEBSTER B. KAY.

CERTIFICATE 0E CORRECTION.

Patent Np. 2,066,686. January 6, 1937.

WEBSTER e. KAY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4, second Column, line 19, claim 10, for the word "stop" read step; and that the said' Letters Patent should be read with this correction. therein that the same may conform to the record of the oase in the yPatent Office.

Signed and sealed this 16th day of March, A. D. 1937.

Henry Van`Ar$da1e (Seal) K. Acting Commissioner of Patents. 

